Concept of Entropy. (Question)

In summary, the conversation discusses the behavior of entropy when a metal is heated and then placed in space. The metal radiates energy in the form of electromagnetic waves, causing a decrease in entropy within the metal. However, the second law of thermodynamics states that entropy always increases in irreversible changes, leading to a discussion about the concept of closed systems and the transfer of entropy between objects. The conversation concludes with the prediction that the increase in entropy in the metal must be equal to or greater than the amount of energy being conducted from the body.
  • #1
amk_dbz
42
0
I have a question about the increasing behavior of entropy.
Suppose we heat a metal (Take for instance Fe) till it radiates energy and then put it in space (No medium). So the metal radiates energy in electromagnetic waves which decreases the entropy of the metal (Due to decrease in internal energy of metal. I hope so :smile:).On the other hand the E.M. waves will keep traveling in space (no medium.It might get absorbed by other objects but still space is quite large?)(The space will be the dump for this energy).So the net entropy change will be a decrease (due to decrease in the system (Fe metal)).But second law of thermodynamics states that entropy always increases for irreversible change.

Where have I gone wrong?

Help will be appreciated.Thank you :smile:.
 
Science news on Phys.org
  • #2
Have you considered the source of your energy you used to heat the metal?
 
  • #3
The closed system here is your whole space - and radiation has entropy, too.
 
  • #4
Drakkith said:
Have you considered the source of your energy you used to heat the metal?

Ok . If i heat the metal by keeping it in contact with body at high temperature T2 then it gives heat q to the metal , So entropy of the body at T2 decreases, right??
 
  • #5
mfb said:
The closed system here is your whole space - and radiation has entropy, too.

Could you explain, please? I do not have deep knowledge in thermodynamics.:confused:
 
  • #6
But second law of thermodynamics states that entropy always increases for irreversible change.
This is true for closed systems only. If you have some way to let entropy flow out, entropy of an object can decrease. This is done all the time when objects cool: They transfer entropy to the environment around them.

In your setup (radiating metal), you need some system where no entropy can leave (or enter) the system to use the second law of thermodynamics. This is "metal + all space where radiation from the metal is". In this system, entropy increases when the metal radiates and cools.
 
  • #7
amk_dbz said:
Ok . If i heat the metal by keeping it in contact with body at high temperature T2 then it gives heat q to the metal , So entropy of the body at T2 decreases, right??
That is correct. If q is the amount of energy being conducted from the body, then the body decreases in entropy by an amount q/T2.
Assuming that all energy is being transported between body and metal. The total entropy in both the metal and the body has to increase according to the Second Law. Therefore, the entropy in the metal as to increase by an amount equal to or greater than q/T2.
The second law has just been used to predict that the increase of entropy in the metal has to be equal to or greater than q/T2. However, the second law by itself doesn't provide the exact value for the increase in entropy of the metal.
The increase in entropy in the metal has two parts. The component of entropy that equals q/T2 is said to be transferred from the body to the metal. The part of the increase in metal entropy that exceeds q/T2 is said to have been created.
 
Last edited:

1. What is the concept of entropy?

The concept of entropy is a measure of the disorder or randomness in a system. It is a thermodynamic quantity that describes the distribution of energy within a system and how likely it is for that energy to be spread out.

2. How is entropy related to the second law of thermodynamics?

The second law of thermodynamics states that the total entropy of a closed system will always increase over time. This means that as energy is transferred or converted, it will become more dispersed and the overall disorder in the system will increase.

3. Why is entropy often referred to as the "arrow of time"?

Entropy is often called the "arrow of time" because it is a one-way process - entropy always increases, never decreases. This means that the direction of time can be determined by the direction in which entropy is increasing.

4. Can entropy be reversed?

In closed systems, entropy cannot be reversed. However, in open systems, where energy can be exchanged with the surroundings, local decreases in entropy are possible, but the overall entropy of the system and its surroundings will still increase.

5. How is entropy related to information theory?

In information theory, entropy is a measure of the uncertainty or randomness in a system. This can be applied to data and communication systems, where a higher entropy indicates a greater amount of information or randomness. Entropy is also used in the calculation of information storage and compression.

Similar threads

Replies
12
Views
1K
  • Thermodynamics
Replies
3
Views
731
Replies
13
Views
1K
  • Thermodynamics
Replies
19
Views
2K
Replies
16
Views
778
Replies
1
Views
470
Replies
17
Views
1K
Replies
3
Views
942
Replies
22
Views
2K
Back
Top